Organic electronic device

ABSTRACT

The present invention relates to organic electronic devices. The devices can include a first electrode, a second electrode, and a substantially organic layer. The substantially organic layer may include a lithium-containing compound, and may be arranged between the first and the second electrode. Also provided herein are organic light emitting diodes, organic solar cells, and organic field effect transistors that include the lithium-containing compound.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application ofPCT/EP2014/061883, filed Jun. 6, 2014, which claims priority to EuropeanApplication No. 13170862.0, filed Jun. 6, 2013. The contents of theseapplications are hereby incorporated by reference.

The present invention relates to an organic electronic device, to aspecific compound for use in such an organic electronic device and to asemiconducting material comprising the inventive compound.

Organic semiconductors can be used to fabricate simple electroniccomponents, e.g. resistors, diodes, field effect transistors, and alsooptoelectronic components like organic light emitting devices, e.g.organic light emitting diodes (OLED). The industrial and economicsignificance of the organic semiconductors and devices using them isreflected in the increasing industry focus on the subject.

OLEDs are based on the principle of electroluminescence in whichelectron-hole pairs, so-called excitons, recombine under the emission oflight. To this end the OLED is constructed in the form of a sandwichstructure wherein at least one organic film is arranged as activematerial between two electrodes, positive and negative charge carriersare injected into the organic material by an external voltage applied onthe electrodes, and the subsequent charge transport brings holes andelectrons to a recombination zone in the organic layer (light emittinglayer, LEL), where a recombination of the oppositely charged chargecarriers to singlet and/or triplet excitons occurs.

The subsequent radiative recombination of excitons causes the emissionof the visible useful light. In order that this light can leave thecomponent, at least one of the electrodes must be transparent.Typically, a transparent electrode consists of conductive oxidesdesignated as TCOs (transparent conductive oxides). Alternatively, avery thin metal electrode can be used. The starting point in themanufacture of an OLED is a substrate on which the individual layers ofthe OLED are applied. If the electrode nearest to the substrate istransparent, the component is designated as a “bottom-emitting OLED”. Ifthe other electrode is designed to be transparent, the component isdesignated as a “top-emitting OLED”. The layers of the OLEDs cancomprise small molecules, polymers, or be hybrid.

Operational parameters of OLEDs are being constantly improved to enhancethe overall power efficiency. One important parameter is the operationvoltage which can be tuned by improving the transport of charge carriersand/or reducing energy barriers such as the injection barriers from theelectrodes. Another important figure is the quantum efficiency, and alsovery relevant is the lifetime of the device. Other organic devices, suchas organic solar cells also require improving in efficiency, whichnowadays, are at best at about 10%.

Like an OLED, an organic solar cell has a stack of organic layersbetween two electrodes. In a solar cell, there must be at least oneorganic layer responsible for the absorption of light and a interfacewhich separates the excitons created by the absorption (photo-active).The interface can be a bi-layer heterojunction, a bulk-heterojunction,or can comprise more layers, e.g., in a step wise interface. Alsosensitizing layers and others can be provided. For increased efficiency,a good charge carrier transport is required, in some device structuresthe transport regions must not absorb light, therefore transport layersand photo-active layers may comprise different materials. Also chargecarrier and/or exciton blocking layers may be employed. Highestefficiency solar-cells are, nowadays, multi-layer solar cells, somedevice structures are stacked (multi-junction solar cells) and connectedby a connecting unit (also called recombination layer); nevertheless,single junction solar cells could have a high performance if the rightmaterials were found. Examples of solar devices are given inUS2009217980, or in US2009235971.

Differently than OLEDs and organic solar cells, transistors do notrequire doping of the entire semiconducting (channel) layer, because theconcentration of available charge carriers is determined by an electricfield supplied by a third electrode (gate electrode). However,convention organic thin film transistors (OTFTs) require very highvoltages to operate. There is a need to lower this operating voltage;such an optimization can be done, e.g. with appropriate injectionlayers.

Organic transistors are also called organic field-effect transistors. Itis anticipated that a large number of OTFTs can be used for example ininexpensive integrated circuits for non-contact identification tags(RFID) but also for screen control. In order to achieve inexpensiveapplications, generally thin-layer processes are required to manufacturethe transistors. In recent years, performance features have beenimproved to such an extent that the commercialization of organictransistors is foreseeable. For example, high field-effect mobilities ofup to 5.5 cm²/Vs for holes have been reported in OTFTs utilizingpentacene (Lee et al., Appl. Lett. 88, 162109 (2006)). A typical organicfield-effect transistor comprises an active layer of organicsemiconducting material (semiconducting layer) which during theoperation forms an electrical conduction channel, a drain electrode anda source electrode which exchange electrical charges with thesemiconducting layer, and a gate electrode which is electricallyisolated from the semiconducting layer by an dielectric layer.

There is a clear need to improve charge carrier injection and/orconductivity in organic electronic devices. Reducing or eliminating thebarrier for charge injection between the electrode and the electrontransport material (ETM) contributes strongly to enhancement of thedevice efficiency. Nowadays, there are two main approaches to reducevoltage and enhance efficiencies of organic electronic devices:improvement of the charge carrier injection and improvement of theconductivity of the transport layers. Both approaches can be used incombination.

For instance, U.S. Pat. No. 7,074,500 discloses a component structurefor an OLED which leads to a greatly improved charge carrier injectionfrom the electrodes into the organic layers. This effect is based onconsiderable band bending of the energy levels in the organic layer atthe interface to the electrodes, as a result of which injection ofcharge carriers on the basis of a tunnel mechanism is possible. The highconductivity of the doped layers also decreases the voltage drop whichoccurs there during operation of the OLED. The injection barriers whichmay occur in OLEDs between the electrodes and the charge carriertransport layers are one of the main causes for an increase in theoperating voltage compared to the thermodynamically justified minimumoperating voltages. For this reason, many attempts have been made toreduce the injection barriers, for example by using cathode materialswith a low work function, for example metals such as calcium or barium.However, these materials are highly reactive, difficult to process andare only suitable to a limited extent as electrode materials. Moreover,any reduction in operating voltage brought about by using such cathodesis only partial.

Metals having low work function, in particular alkali metals such as Liand Cs, are often used either as the cathode material or the injectionlayer to promote electron injection. They have also widely been used aselectrical dopants in order to increase the conductivity of the ETM, seee.g. U.S. Pat. Nos. 6,013,384, 6,589,673. Metals like Li or Cs provide ahigh conductivity in matrixes which are difficult to dope otherwise(e.g. BPhen, Alq3).

However, the use of low work function metals has several disadvantages.It is well known that the metals can easily diffuse through thesemiconductor, eventually arriving at the optically active layer andquenching the excitons, thereby lowering the efficiency of the deviceand the lifetime. Another disadvantage is their high susceptibility tooxidation upon exposure to air. Therefore, devices using such metals asdopants, injection or cathode material require rigorous exclusion of airduring production and rigorous encapsulation afterwards. Anotherwell-known disadvantage is that higher doping concentration of thedopant exceeding 10 mol. % may increase the undesired absorption oflight in the doped charge transport layers. Yet another problem is highvolatility of many simple redox dopants like Cs, leading tocross-contamination in the device assembling process making their use indevice fabrication tools difficult.

Another approach to replace metals as n-dopants and/or injectionmaterials for ETM is the use of compounds with strong donor properties,such astetrakis(1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinato)ditungsten(II) (W₂(hpp)₄) or Co(Cp*)₂ (US2009/0212280, WO2003/088271) which havesimilar or slightly less doping/injecting ability in comparison withalkaline earth metals. These compounds have more favourably lowervolatilities than alkali metals and their diffusion through the dopedlayers is strongly impeded by their high molar mass, however, due totheir still high electron donating capability, they are still undergoingrapid decay upon exposure to air, what makes their handling in deviceproduction difficult too.

Another alternative approach consists in mixing metal organic complexessuch as lithium quinolate (LiQ) into an electron transport layer. Theexact mechanism of the voltage improvement is not yet sufficientlyclarified. Devices using LiQ as electrical dopant for improving voltagestill show significantly higher operating voltages in comparison withdevices doped with strongly reductive metals or with strongly reductiveorganic redox dopants.

Therefore, it is very desirable to provide materials which possess highdoping/charge injection capability, allowing for highly efficientorganic electronic devices, substantially preserving the long-termstability of the device and which are infinitely stable in air.

It is therefore an objective of the present invention to provide anorganic electronic device, which overcomes state of the art limitationsmentioned above and have improved performance compared to electronicdevices of the prior art in terms of reduced operating voltage andhigher power efficiency. Another object of the invention is a compoundenabling the organic electronic devices with improved performance. Athird object of the invention is a semiconducting material comprisingthe inventive compound.

SUMMARY OF THE INVENTION

The first object is achieved by an organic electronic device, comprisinga first electrode, a second electrode, and a substantially organic layercomprising a compound according to formula (I) between the first and thesecond electrode:

wherein A¹ is a C₆-C₃₀ arylene or C₂-C₃₀ heteroarylene comprising atleast one atom selected from O, S and N in an aromatic ring and each ofA² and A³ is independently selected from a C₆-C₃₀ aryl and C₂-C₃₀heteroaryl comprising at least one atom selected from O, S and N in anaromatic ring and wherein either

-   -   i) A¹ is C₂-C₃₀ heteroarylene comprising at least one atom        selected from O, S and N in an aromatic ring    -   and/or    -   ii) at least one of A² and A³ is C₂-C₃₀ heteroaryl comprising at        least one atom selected from O, S and N in an aromatic ring.

The aryl, heteroaryl, arylene or heteroarylene may be unsubstituted orsubstituted with groups comprising C and H or with a further LiO group.It is supposed that the given C count in an aryl, heteroaryl, arylene orarylene group includes also all substituents present on the said group.

It is to be understood that the term substituted or unsubstitutedarylene or heteroarylene stands for a divalent radical derived fromsubstituted or unsubstituted arene or heteroarene, wherein the bothstructural moieties adjacent in formula (I) to A¹ (the OLi group and thePOA²A³ group) are attached directly to an aromatic ring of the aryleneor heteroarylene group. Examples of simple arylenes are o-, m- andp-phenylene; polycyclic arylenes may have their adjacent groups attachedeither on the same aromatic ring or on two different aromatic rings.

In case of (hetero)arylenes derived from the polycyclic (hetero)arenes,the definition of o-, m- and p-substitution is generalized as follows.(Hetero)arylenes, wherein OLi and POA²A³ are attached to two neighbourcarbon atoms that are directly attached to each other in the samearomatic ring, are understood as o-(hetero)arylenes. All(hetero)arylenes having the substituents OLi and POA²A³ attached to theopposite sides of a rigid arene structure so that the bonds to thesesubstituents are parallel, are defined as p-(hetero)arylenes, whereas inm-(hetero)arylenes, there is at least one atom between the C atoms towhich OLi and POA²A³ are attached and the angle between the bondsattaching the OLi and the POA²A³ moieties is different from 180° (in therigid aromatic structures) or variable, e.g. in (hetero)arylenesconsisting of two or more rigid (hetero)arylene substructures boundtogether by single bonds.

Examples of generalized p-(hetero)arylenes are naphthalene-1,4-diyl,naphthalene-1,5-diyl, naphthalene-2,6-diyl, 1,1′-biphenyl-4,4′-diyl,pyridine-2,5-diyl, quinoline-2,6-diyl, quinoline-3,7-diyl,quinoline-4,8-diyl, quinoline-5,8-diyl. Examples of generalizedm-(hetero)arylenes are naphthalene-1,3-diyl, naphthalene-1,6-diyl,naphthalene-1,7-diyl, naphthalene-1,8-diyl, naphthalene-2,7-diyl,1,1′-biphenyl-3,4′-diyl, 1,1′-biphenyl-2,4′-diyl,1,1′-biphenyl-2,4′-diyl, 1,1′-biphenyl-2,3′-diyl,1,1′-biphenyl-3,3′-diyl, 1,1′-biphenyl-2,2′-diyl, pyridine-2,6-diyl,pyridine-2,4-diyl, pyridine-3,5-diyl, quinoline-2,8-diyl,thiophene-2,4-diyl, thiophene-2,5-diyl, furan-2,4-diyl, furan-2,5-diyl.

Preferably, A¹ is C₆-C₁₂ arylene or C₂-C₁₂ heteroarylene. Evenpreferably, each of A²-A³ is independently selected from a C₆-C₁₀ arylor C₂-C₁₂ heteroaryl. More preferably, both A² and A³ are independentlyselected from phenyl and pyridyl. Most preferably, A¹ is phenylene orpyridine-diyl.

In one preferred embodiment, the substantially organic layer comprisesan electron transport matrix compound.

In a further preferred embodiment, the electron transport matrixcomprises an imidazole or a P═O functional group.

Moreover, the compound according to formula (I) and the electrontransport matrix compound are preferably present in the substantiallyorganic layer in the form of a homogeneous mixture.

Furthermore, the organic electronic device may be selected from anorganic light emitting diode, organic solar cell and organic fieldeffect transistor.

Preferred is an organic electronic device wherein the device is anorganic light emitting diode with the first electrode being an anode,the second electrode being a cathode, and the device further comprisinga light emitting layer between the anode and the cathode and wherein thesubstantially organic layer is comprised between the cathode and theLEL. Alternatively or in addition, the LEL of the organic electronicdevice comprises a light emitting polymer.

The second object of the present invention is achieved by compoundaccording to formula (I)

wherein A¹ is a C₆-C₃₀ arylene or C₂-C₃₀ heteroarylene comprising atleast one atom selected from O, S and N in an aromatic ring and each ofA² and A³ is independently selected from a C₆-C₃₀ aryl and C₂-C₃₀heteroaryl comprising at least one atom selected from O, S and N in anaromatic ring and wherein either

-   -   i) A¹ is C₂-C₃₀ heteroarylene comprising at least one atom        selected from O, S and N in an aromatic ring    -   and/or    -   ii) at least one of A² and A³ is C₂-C₃₀ heteroaryl comprising at        least one atom selected from O, S and N in an aromatic ring.

The aryl, heteroaryl, arylene or heteroarylene may be unsubstituted orsubstituted with groups comprising C and H or with a further LiO group.It is supposed that the given C count in an aryl, heteroaryl, arylene orarylene group includes also all substituents present on the said group.

Preferably, A¹ is C₆-C₁₂ arylene or C₂-C₁₂ heteroarylene. Evenpreferably, each of A²-A³ is independently selected from a C₆-C₁₀ arylor C₂-C₁₂ heteroaryl. More preferably, both A² and A³ are independentlyselected from phenyl and pyridyl. Most preferably, A¹ is phenylene orpyridine-diyl.

Preferred use of the compound according to formula (I) in an organicelectronic device is as an electrical dopant in and/or adjacent anelectron transport layer of the device.

The third object of the present invention is achieved by an electricallydoped semiconducting material comprising at least one electron transportmatrix compound and at least one compound according to formula (I).

DETAILED DESCRIPTION OF THE INVENTION

Preferably, the compound according to formula (I) is used in transportand/or injection layers, more preferably in an electron transport layerand/or electron injection layer, most preferably in the form of theelectrically doped semiconducting material according to the invention.

The chemical compounds according to formula (I) are air-stable andcapable to be evaporated without decomposition. They are also soluble ina variety of solvents. This makes the compounds according to formula (I)particularly easy to use in manufacturing processes.

The inventive organic electronic device preferably comprises a layeredstructure including a substrate, an anode and a cathode, the at leastone substantially organic layer being disposed within the layeredstructure between the anode and the cathode.

The substantially organic layer may further comprise an electrontransport matrix compound. Preferably, the electron transport matrixcompound and compound according to formula (I) form a homogeneousmixture. Compound (I) constitutes preferably 10 weight % or more of thesubstantially organic layer. More preferred is 40 wt. % or more. For anelectron transport layer, it is however preferred that the electrontransport matrix is the main component of the layer.

As matrix materials for electron transport layers, use may be made forexample of fullerenes, such as for example C₆₀, oxadiazole derivatives,such as for example2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, quinoline-basedcompounds such as for example bis(phenylquinoxalines), oroligothiophenes, perylene derivatives, such as e.g.perylenetetracarboxylic acid dianhydride, naphthalene derivatives suchas e.g. naphthalenetetracarboxylic acid dianhydride, or other similarcompounds known as matrices in electron transport materials.

It is preferred that the electron transport material comprises aphosphine oxide or imidazole functional groups.

Compounds well suitable as electron transport materials are compoundsfrom:

-   -   US2007/0138950, preferentially, compounds (1) and (2) on page        22, compounds (3), (4), (5), (6), and (7) on page 23, compounds        (8), (9), and (10) on page 25, and compounds (11), (12), (13),        and (14) on page 26, which compounds are incorporated herein by        reference;    -   US2009/0278115 A1, preferentially, compounds (1) and (2) on page        18, which compounds are incorporated herein by reference;    -   compounds from US2007/0018154, preferentially the compounds of        claim 10, formula 1-1, 1-2, 1-3, 1-4, 1-5, 1-6 on page 19, 1-7        to 1-146 on pages 20 to 26. Compounds from US2008/0284325 A1,        preferentially compounds on page 4:        2-(4-(9,10-diphenylanthracen-2-yl)phenyl)-1-phenyl-1H-benzo[d]imidazole,        2-(4-(9,10-di([1,1′-biphenyl]-2-yl)anthracen-2-yl)phenyl)-1-phenyl-1H-benzo[d]imidazole,        2-(4-(9,10-di(naphthalen-1-yl)anthracen-2-yl)phenyl)-1-phenyl-1H-benzo[d]imidazole,        2-(4-(9,10-di(naphthalen-2-yl)anthracen-2-yl)phenyl)-1-phenyl-1H-benzo[d]imidazole,        2-(4-(9,10-di([1,1′:3′,1″-terphenyl]-5′-yl)anthracen-2-yl)phenyl)-1-phenyl-1H-benzo[d]imidazole,        and the compound on page 5, which compounds are incorporated        herein by reference;    -   naphthacene derivatives from US2007/0222373, preferentially,        compounds (A-1) and (A-2) from page 17, compounds (A-3) from        page 18 and (A-4) from page 19, which compounds are incorporated        herein by reference;    -   compounds from US2008/0111473, preferentially, compound 1 on        page 61, compound 2 on page 62, compounds 3 and 4 on page 63,        compound 5 on page 64, and compound 6 on page 65, which        compounds are incorporated herein by reference;    -   compound H-4 from page 20, and compounds (1) and (2) of page 12        of US2010/0157131, which compounds are incorporated herein by        reference;    -   compounds from US2010/0123390, according to general formula (1),        preferentially, compounds H4, H5 p. 21, H7 p. 22, H11, H12,        H13 p. 23, H16, and 1118 p. 24, which compounds are incorporated        herein by reference;    -   US2007/0267970, preferentially        2-([1,1′-biphenyl]-4-yl)-1-(4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)-2,7a-dihydro-1H-benzo[d]imidazole        (compound 1),        2-([1,1′-biphenyl]-2-yl)-1-(4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)-2,7a-dihydro-1H-benzo[d]imidazole        (compound 2). Compound (C-1) from US2007/0196688, p. 18, which        is incorporated herein by reference;

Other suitable compounds are7-(4′-(1-phenyl-1H-benzo[d]imidazol-2-yl)-[1,1′-biphenyl]-4-yl)dibenzo[c,h]acridine,(3-(dibenzo[c,h]acridin-7-yl)phenyl)diphenylphosphine oxide (assigned A1in examples of the present application),(4-(dibenzo[c,h]acridin-7-yl)phenyl)diphenylphosphine oxide (assigned A2in examples of the present application),7-(4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)dibenzo[c,h]acridine.

Suitable hole transport materials (HTM) can be, for instance, HTM fromthe diamine class, where a conjugated system is provided at leastbetween the two diamine nitrogens. Examples areN4,N4′-di(naphthalen-1-yl)-N4,N4′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(HTM1),N4,N4,N4″,N4″-tetra([1,1′-biphenyl]-4-yl)-[1,1′:4′,1″-terphenyl]-4,4″-diamine(HTM2),N4,N4″-di(naphthalen-1-yl)-N4,N4″-diphenyl-[1,1′:4′,1″-terphenyl]-4,4″-diamine(HTM3), The synthesis of diamines is well described in literature; manydiamine HTMs are readily commercially available.

It will be understood that the aforementioned matrix materials may alsobe used in a mixture with one another or with other materials in thecontext of the invention. It will be understood that use may also bemade of suitable other organic matrix materials which havesemiconductive properties.

In another preferred embodiment, the substantially organic layer ispresent in a pn junction, the pn junction having at least two layers,namely a p- and n-layer, and optionally an interlayer i in between,wherein the interlayer i and/or the n-layer is (are) the substantiallyorganic semiconducting layer.

The organic electronic device may additionally comprise a polymersemiconducting layer.

Most preferably, the organic electronic device is a solar cell or alight emitting diode.

The organic electronic device may be also a field effect transistorcomprising a semiconducting channel, a source electrode, and a drainelectrode, the substantially organic layer being provided in between thesemiconducting channel and at least one of the source electrode and thedrain electrode.

In a further most preferred embodiment, the substantially organic layercomprising the chemical compound according to formula (I) is an electroninjection layer and/or an electron transport layer.

Any layers of the inventive organic electronic device, especially thesubstantially organic layer can be deposited by known techniques, suchas vacuum thermal evaporation (VTE), organic vapour phase deposition,laser induced thermal transfer, spin coating, blade or slit coating,inkjet printing, etc. A preferred method for preparing the organicelectronic device according to the invention is vacuum thermalevaporation.

Surprisingly, it was found that the inventive organic electronic deviceovercomes disadvantages of prior art devices and has in particular animproved performance compared to electronic devices of the prior art,for example with regard to efficiency.

Injection Layer

In a preferred embodiment, the substantially organic layer, having thecompound according to formula (I) as its main component, is adjacent toa cathode, preferably between a cathode and one of an ETL (electrontransporting layer) or HBL (hole blocking layer). The present inventionhas the advantages that, especially for non-inverted structures, thesimplest form is also the one with a significantly improved performancecompared to the structure not using an injection layer. The compoundaccording to formula (I) can be used as a pure layer and is thenpreferably the only layer between an electron transporting layer (ETL orHBL) and the cathode. In this regard for an OLED the EML (emitter layer)and ETL matrix can be the same if the emission zone is far from thecathode. In another embodiment, the ETL and the EML are layers ofdifferent composition, preferably of a different matrix.

Such a pure layer as injection layer in organic electronic devices has apreferable thickness between 0.5 nm and 5 nm.

The thickness of the layer comprising the compound according to formula(I) is the nominal thickness, such thickness is usually calculated fromthe mass deposited on a certain area by the knowledge of the material'sdensity. For example, with vacuum thermal evaporation VTE, the nominalthickness is the value indicated by the thickness monitor equipment. Inreality, since the layer is not homogeneous and not flat at least at oneinterface, its final thickness is difficult to measure, in this case,the average value can be used. The cathode in this regard is aconductive layer having optionally any surface modifications to modifyits electrical properties, e.g. to improve its work-function orconductivity. Preferably, the cathode is a double layer, more preferablyit is a single layer to avoid complexity.

Semiconducting Layer

It is even preferred that the organic layer is an electron transportlayer adjacent to the cathode and comprising the compound according toformula (I). If the ETL is directly adjacent to the cathode, thissimplification has the advantage that no additional injection layer isrequired. Alternatively, an additional injection layer can be providedbetween the ETL and the cathode. This additional layer can be a layerhaving the chemical compound according to formula (I) as its maincomponent, as already illustrated above. In one even preferredembodiment, the ETL is beneath the cathode (no other layer in between)wherein the cathode is the top electrode, which is formed after formingthe ETL (non-inverted structure).

For an OLED the LEL (light emitting layer) and ETL matrix can be thesame if the emission zone is far from the cathode. In anotherembodiment, the ETL and the LEL are layers of different composition,preferably of a different matrix.

Polymer Hybrid OLED or Solar Cell

In a further preferred embodiment the substantially organic layercomprising the chemical compound according to formula (I) is used incombination with a polymer semiconductor, preferably between a cathodeand a polymer layer, wherein the polymer layer preferably comprises theoptoelectronic active region of the device (emitting region of an OLEDor the absorbing region of a solar cell). All alternatives of layerscomprising the chemical compound according to formula (I) or beingcomposed thereof can be used in combination with that polymer layer.Exemplary alternative layers can be an injection layer being composed ofthe chemical compound according to formula (I), an injection layercomprising the chemical compound and a metal, an electron transportlayer having the chemical compound with or without a metal. Theelectronic interface to the cathode is then strongly improved given thehigh electron injection capability of the chemical compound (I).

Electrical Doping

The invention can be used as an alternative to conventional redox dopingof organic semiconducting layers. By using the term redox doping it ismeant specific case of electrical doping using strong oxidizing orreducing agents as explained above. This doping can also be calledcharge transfer doping. It is known that the redox doping increases thedensity of charge carriers of a semiconducting matrix towards the chargecarrier density of the undoped matrix. An electrically dopedsemiconductor layer may also have an increased effective mobility incomparison with the undoped semiconductor matrix.

US2008227979 discloses in detail the doping of organic transportmaterials, also called matrix, with inorganic and with organic dopants.Basically, an effective electronic transfer occurs from the dopant tothe matrix increasing the Fermi level of the matrix. For an efficienttransfer in a p-doping case, the LUMO energy level of the dopant ispreferably more negative than the HOMO energy level of the matrix or atleast slightly more positive, not more than 0.5 eV, to the HOMO energylevel of the matrix. For the n-doping case, the HOMO energy level of thedopant is preferably more positive than the LUMO energy level of thematrix or at least slightly more negative, not lower than 0.5 eV, to theLUMO energy level of the matrix. It is further more desired that theenergy level difference for energy transfer from dopant to matrix issmaller than +0.3 eV.

Typical examples of doped hole transport materials are:copperphthalocyanine (CuPc), which HOMO level is approximately −5.2 eV,doped with tetrafluoro-tetracyanoquinonedimethane (F4TCNQ), which LUMOlevel is about −5.2 eV; zincphthalocyanine (ZnPc) (HOMO=−5.2 eV) dopedwith F4TCNQ; a-NPD(N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine) doped withF4TCNQ; a-NPD doped with2,2′-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (PD1); a-NPDdoped with2,2′,2″-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile)(PD2). PD2 was used in the examples of the present application asp-dopant.

One of the preferred modes of the invention is an OLED with the holetransporting side of OLED comprising a p-dopant and the electrontransporting side comprising the material according to Formula (I). Forexample: an OLED with a p-doped HTL and an ETL with a ETM and thematerial according to Formula (I).

SHORT SUMMARY OF THE FIGURES

FIG. 1 illustrates a first embodiment of an inventive organic electronicdevice;

FIG. 2 illustrates a second embodiment of an inventive organicelectronic device;

FIG. 3 shows a third embodiment of an inventive organic electronicdevice.

FIGS. 4 and 5 show current-voltage and current-efficiency curves of aninventive device comprising compound D1 in comparison with devicescomprising previous art compounds C2 and C3, all in the matrix A1.

FIGS. 6 and 7 show current-voltage and current-efficiency curves of aninventive device comprising compound D1 in comparison with a devicecomprising previous art compound C2, both in the matrix A2.

FIGS. 8 and 9 show current-voltage and current-efficiency curves of aninventive device comprising compound D1 in comparison with a devicecomprising previous art compound C3, both in the matrix A3.

ORGANIC ELECTRONIC DEVICES

FIG. 1 illustrates a first embodiment of an inventive organic electronicdevice in the form of a stack of layers forming an OLED or a solar cell.In FIG. 1, 10 is a substrate, 11 is an anode, 12 is an EML or anabsorbing layer, 13 is a EIL (electron injection layer), 14 is acathode.

The layer 13 can be a pure layer of a compound according to formula (I).At least one of the anode and cathode is at least semi-transparent.Inverted structures are also foreseen (not illustrated), wherein thecathode is on the substrate (cathode closer to the substrate than theanode and the order of the layers 11-14 is reversed). The stack maycomprise additional layers, such as ETL, HTL, etc.

FIG. 2 represents a second embodiment of the inventive organicelectronic device in the form of a stack of layers forming an OLED or asolar cell. Here, 20 is a substrate, 21 is an anode, 22 is an EML or anabsorbing layer, 23 is an ETL, 24 is a cathode. The layer 23 comprisesan electron transport matrix material and a compound according toformula (I).

FIG. 3 illustrates a third embodiment of the inventive device in theform of an OTFT, with semi-conductor layer 32, a source electrode 34 anda drain electrode 35. An unpatterned (unpatterned between the source anddrain electrodes) injection layer 33 provides charge carrier injectionand extraction between the source-drain electrodes and semi-conductinglayer. OTFT also comprises a gate insulator 31 (which could be on thesame side as the source drain electrodes) and a gate electrode 30, whichgate electrode 30 is on the side of the layer 31 which is not in contactwith the layer 32. Obviously, the whole stack could be inverted. Asubstrate may also be provided. Alternatively, insulator layer 31 may bethe substrate.

EXAMPLES

Following compounds were used as electron transporting matrices fortesting the effects of inventive compounds:

A1 is described in the application PCT/EP2012/004961 (WO2013/079217,page 51-52), A2 is described in the application WO2011/154131 (Examples4 and 6), A3 (CAS number 561064-11-7) is commercially available.

Synthetic Procedure for Preparing the Compounds of Formula (I)

All reactions were performed under inert atmosphere. Commercialreactants and reagents were used without further purification. Reactionsolvents tetrahydrofurane (THF), acetonitrile (AcN) and dichloromethane(DCM) were dried by a solvent purification system (SPS).

Example 1: Synthesis of lithium 2-(diphenylphosphoryl)pyridin-3-olate(1) Step 1: diphenyl(pyridin-2-yl)phosphine oxide

2-fluoropyridine 2.50 g, 1.0 eq, 25.8 mmol potassium diphenylphosphide51.5 mL, 1.0 eq, 25.8 mmol THF 50 mL DCM 80 mL hydrogen peroxide 25 mLhexane 20 mL

Fluoropyridine was dissolved in dry THF. The potassium diphenylphosphidesolution was added drop wise during one hour at room temperature. Theresulting orange solution was stirred overnight at room temperature. Thesolvent was removed under reduced pressure and the residue dissolved indichloromethane. Hydrogen peroxide was added slowly at 0° C. The mixturewas stirred overnight at room temperature. The solvent was removed underreduced pressure and the residue treated with hexane. The resultingsolid was filtered off, washed with hexane and dried in vacuum.

Yield: 2.2 g (31%), HPLC-MS purity 98.0%.

Step 2: (3-hydroxypyridin-2-yl)diphenylphosphine oxide

diphenyl(pyridin-2-yl)phosphine oxide 2.0 g, 1.0 eq., 7.2 mmol2-isopropoxy-4,4,5,5-tetramethyl-1,3,2- 4.35 mL, 3.0 eq., 21.5 mmoldioxaborolane Lithium diisopropylamide (LDA) 9.56 mL, 2.0 eq., 14.3 mmolTHF 50 mL Chloroform 50 mL Hydrogen peroxide 10 mL DCM 15 mL

The starting material was dissolved in dry THF and cooled to −78° C. Theborolane was added and the mixture stirred for 20 min. The LDA solutionwas added drop wise and the temperature was allowed to rise slowly toroom temperature. The reaction was stirred for 3 days at roomtemperature. The solvent was removed under reduced pressure and theresidue was dissolved in chloroform. Hydrogen peroxide was added slowlyat 0° C. and the mixture was stirred overnight at room temperature. Themixture was extracted with chloroform and brine. The organic phase wasdried over magnesium sulphate and the solvent removed under reducedpressure. The residue was dissolved in DCM and precipitated with hexane.The solid was filtered off, washed with hexane and dried in vacuum.

Yield: 1.4 g (67%), GCMS purity 100%, structure confirmed by ¹H-NMR, δ(ppm)=11.48 (s, 1H, OH), 8.25 (d X from ABX system, J=4.5 Hz, 1H), 7.90(dd, J=12 Hz and 7.5 Hz, 4H), 7.58 (br t, J=7 Hz, 2H), 7.50 (td, J=7.5Hz and 3 Hz, 4H), 7.30 (ddd, B from ABX system, 1H), 7.24 (br dd, A fromABX system, 1H).

Step 3: lithium 2-(diphenylphosphoryl)pyridin-3-olate (1)

(3-hydroxypyridin-2-yl)- 1.0 g, 1.0 eq., 3.4 mmol diphenylphosphineoxide Lithium tert-butoxide 0.27 g, 1.0 eq., 3.4 mmol Acetonitrile 40 mL

The starting material was suspended in dry acetonitrile. The lithiumtert-butoxide was added at room temperature and the mixture was heatedat reflux for 13 hours. The solid was filtered off, washed withacetonitrile and dried in vacuum.

Yield: 0.865 g (87%), TGA-DSC: m.p. 442° C.

Analytical data (after sublimation):

TGA-DSC: m.p. 445° C.

Elemental analysis: 67.6% C-content (theory 67.79%), 4.48% H-content(theory 4.35%), 4.64% N-content (theory 4.65%)

Example 2: lithium 7-(diphenylphosphoryl)quinolin-8-olate (2)

Step 1: synthesis of quinolin-8-yl diphenylphosphinate

10 g 8-hydroxyquinoline were dissolved in 170 mL dry THF. 17.9 g (1.1eq.) diphenylphosphoryl chloride and 7.7 g (1.1 eq.) diisopropylaminewere added at room temperature. After stirring overnight, the reactionmixture was filtered, then evaporated to dryness and treated with 40 mLhexane. 23.5 g white solid were obtained (98% yield), GCMS gives 100%purity.

Step 2: synthesis of lithium 7-(diphenylphosphoryl)quinolin-8-olate (2)

7 g quinolin-8-yl diphenylphosphinate from the previous step weredissolved in 120 mL dry THF under argon. The clear solution was cooledto −80° C. 14.9 mL (1.1 eq.) of 1.5 M lithium diisopropylamide solutionin cyclohexane were added dropwise as to the starting compound. Thereaction mixture was allowed to return to room temperature overnight andfurther stirred for one entire week. Then, an addition of 100 mLn-hexane afforded a precipitate that was isolated by filtration andfurther purified by a hot slurry wash in 120 mL acetonitrile. 2.43 g(34% yield) of a beige solid were obtained and further purified throughgradient sublimation.

Example 3: lithium 2-(diphenylphosphoryl)quinolin-3-olate (3)

Step 1: synthesis of diphenyl(quinolin-2-yl)phosphine oxide

4 g 2-chloroquinoline (1 eq.) were dissolved in 50 mL dry THF underargon. To this solution, 48.9 mL (1 eq.) of commercial 0.5 M solution ofpotassium diphenylphosphite in THF were added at room temperature over90 minutes. After stirring overnight at room temperature, the solutionwas evaporated to dryness and the residue suspended in 80 mLdichloromethane and treated with 20 mL of 30 wt. % hydrogen peroxideaqueous solution. After 3 h stirring at room temperature, the organicphase was washed twice with 30 mL brine and twice with 30 mL distilledwater, dried over magnesium sulfate, filtered and evaporated. Theresidue was precipitated from dichloromethane/hexane to obtain 4.62 g(57% yield) of a pale yellow solid. HPLC showed 99.2% purity.

Step 2: synthesis of (3-hydroxyquinolin-2-yl)diphenylphosphine oxide

4.5 g (1 eq.) diphenyl(quinolin-2-yl)phosphine oxide were dissolved in50 mL dry TI-IF under argon. The solution was cooled at −80° C., and 8.4mL (3 eq.) 2-isopropoxy-4,4′,5,5′-tetramethyl-1,3,2-dioxaborolane (neat)were added with a syringe. After 20 minute stirring at −80° C., 18.3 mL(2 eq.) of 1.5 M lithium diisopropylamide solution in cyclohexane wereadded dropwise. The reaction mixture was let return to room temperatureover the weekend, then evaporated to dryness and redissolved in 60 mLdichloromethane. The suspension was treated with 10 mL 30% aqueoushydrogen peroxide over 24 h. After washing with 30 mL brine and 50 mLdistilled water, the organic phase was dried over magnesium sulfate,filtered and evaporated. The residue was dissolved in 30 mLdichloromethane and washed twice with 30 mL of saturated ammoniumchloride solution, then with 2 mL 1M hydrochloric acid for acidifyingthe aqueous phase before drying and evaporating. The evaporation residuewas slurry washed in 30 mL acetonitrile to afford 2.8 g (60% yield) of abright yellow solid. GCMS showed 96% purity.

Step 3: synthesis of lithium 2-(diphenylphosphoryl)quinolin-3-olate (3)

2.7 g (1 eq.) (3-hydroxyquinolin-2-yl)diphenylphosphine oxide weresuspended in 40 mL dry acetonitrile. 0.63 g (1 eq.) lithiumtert-butoxide were added in one portion as a solid. The suspensionturned yellow. After 4 h under reflux, the suspension was cooled to roomtemperature and the solid isolated, washed with a minimal amountacetonitrile and dried. Obtained 2.44 g (89% yield) of a beige solid,which was further purified by gradient sublimation.

Example 4: lithium 3-(diphenylphosphoryl)pyridin-2-olate (4)

Step 1: synthesis of diphenyl(pyridin-3-yl)phosphine oxide

110 mL of a 0.5 M potassium diphenylphosphite solution in THF werediluted with 110 mL dry THF under argon. 8 g 3-fluoropyridine were addeddropwise at 0° C. to this solution during 30 minutes. The mixture wasstirred overnight at room temperature, then evaporated to dryness andredissolved in 150 mL dichloromethane. The mixture was treated with 17mL 30% aqueous hydrogen peroxide overnight. The organic phase was thenwashed twice with 30 mL brine and three times with 40 mL distilledwater, then dried over magnesium sulfate, filtered and evaporated. Theresulting oil was precipitated by addition 30 mL hexane and anultrasound treatment. Isolated 12.1 g of a white solid (79% yield), GCMSshowed 100% purity.

Step 2: synthesis of (2-hydroxypyridin-3-yl)diphenylphosphine oxide

5 g diphenyl(pyridin-3-yl)phosphine oxide were dissolved in 100 mL dryTHF under argon and the solution was cooled to −80° C. 10.9 mL (3 eq.)2-isopropoxy-4,4′,5,5′-tetramethyl-1,3,2-dioxaborolane (neat) were addedwith a syringe. After 25 minute stirring at −80° C., 23.8 mL (2 eq.) of1.5 M lithium diisopropylamide solution in cyclohexane were addeddropwise. The reaction mixture was let return to room temperature overfive days, then evaporated to dryness and redissolved in 200 mLdichloromethane. The suspension was treated by 10 mL 30 wt. % aqueoushydrogen peroxide over 24 h. After washing twice with 30 mL brine andthree times with 30 mL distilled water, the organic phase was dried overmagnesium sulfate, filtered and evaporated. The residue was slurrywashed with 50 mL hexane. Obtained 3.8 g (72% yield) of a pale yellowsolid. Used without further purification.

Step 3: synthesis of lithium 3-(diphenylphosphoryl)pyridin-2-olate (4)

3.6 g (2-hydroxypyridin-3-yl)diphenylphosphine oxide were suspended in150 mL acetonitrile. After addition 0.98 g (1 eq.) lithiumtert-butoxide, the mixture was heated overnight under reflux. Afterreturn to room temperature, the formed precipitate was isolated andwashed with a minimal amount acetonitrile. Obtained 3.3 g (90%) of awhite solid that was further purified by gradient sublimation.

DEVICE EXAMPLES

Lithium 2-(diphenylphosphoryl)phenolate (C2), described in an earlierapplication PCT/EP/2012/074127, and the well-known lithium8-hydroxyquinolinolate (LiQ, C3) were used as comparative electricaln-dopants; lithium 2-(diphenylphosphoryl)pyridin-3-olate (1), referredto as D1, lithium 2-(diphenylphosphoryl)quinolin-3-olate (3), referredto as D5, and lithium 3-(diphenylphosphoryl)pyridin-2-olate (4),referred to as D6, were used as inventive n-dopants.

Example 1

A blue emitting device was made on a commercially available glasssubstrate with deposited indium tin oxide (ITO) 90 nm thick layer as ananode. A 10 nm layer of HTM3 doped with2,2′,2″-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile)(PD2) (matrix to dopant weight ratio of 92:8) was subsequently depositedas hole injection and transport layer, followed by a 120 nm undopedlayer of HTM3. Subsequently, a blue fluorescent emitting layer of ABH113(Sun Fine Chemicals) doped with NUBD370 (Sun Fine Chemicals) as anemitter (matrix dopant ratio of 97:3 wt. %) was deposited with athickness of 20 nm. A 36 nm thick ETL having a composition given in theTable 1 was deposited on the emitting layer. A 1 nm thick layer oflithium quinolate (LiQ) followed the ETL, followed by 100 nm thickaluminium layer as a cathode.

The results are shown in the Table 1.

TABLE 1 Current Voltage at efficiency 10 mA/cm² at 10 mA/cm² CIE CIE ETL[V] [cd/A] 1931 x 1931 y A1:D1 (60:40 wt. %) 4.4 6.4 0.14 0.10 A1:C2(60:40 wt. %) 4.3 5.3 0.14 0.09 A1:C3 (60:40 wt. %) 4.6 4.9 0.14 0.10A2:D1 (50:50 wt. %) 4.9 5.6 0.14 0.10 A2:C2 (50:50 wt. %) 4.7 5.5 0.140.09 A3:D1 (50:50 wt. %) 4.6 5.5 0.14 0.11 A3:C3 (50:50 wt. %) 4.5 4.90.14 0.11 A1:D5 (60:40 wt. %) 4.4 6.6 0.14 0.11 A1:D6 (60:40 wt. %) 4.55.6 0.14 0.11

Advantages of the Invention

Surprisingly, an increase of the OLED efficiency and a decrease of theoperating voltage were observed in experimental devices comprising theinventive semiconducting materials.

Inventive devices comprising compounds of formula (I) as ETL additivesperform better than devices using known LiQ (C3) and at least equallywell as devices comprising compound C2 with a similar structure withouta heteroatom. Inventive compounds of formula (I) thus significantlybroaden the offer of additives for improving electron transport and/orelectron injection in organic electronic devices and allow furtherimproving and optimizing performance of organic electronic devicesbeyond limits known in the art.

The features disclosed in the foregoing description, the claims and inthe drawings may both separately and in any combination thereof, bematerial for realising the invention in diverse forms thereof.

ABBREVIATIONS USED THROUGHOUT THE APPLICATION

OLED organic light emitting device

OTFT organic thin film transistor

EL electroluminescence, electroluminescent

ETL electron transport layer

ETM electron transport material

HTL hole transport layer

EBL electron blocking layer

HBL hole blocking layer

LEL light emitting layer

EIL electron injecting layer

HIL hole injecting layer

VTE vacuum thermal evaporation

HOMO highest occupied molecular orbital

LUMO lowest unoccupied molecular orbital

¹H-NMR proton magnetic resonance

EI-MS electron impact mass spectroscopy

GCMS gas chromatography (combined with) mass spectroscopy

HPLC-MS high performance liquid chromatography-mass spectroscopy

BPhen bathophenanthroline

Alq3 aluminium tris(8-hydroxyquinolinolate)

LiQ lithium 8-hydroxyquinolinolate

THF tetrahydrofuran

DCM dichloromethane

eq. Equivalent

wt. % weight percent

mol. molar (e.g. percent)

TGA-DSC thermogravimetric analysis-differential scanning calorimetry

TCO transparent conductive oxide

RFID radio-frequency identification

The invention claimed is:
 1. An organic electronic device comprising afirst electrode, a second electrode, and a substantially organic layerarranged between the first and the second electrode, wherein thesubstantially organic layer comprises a compound according to formula(I):

wherein A¹ is a pyridine-diyl, and each of A² and A³ is independentlyselected from a C₆-C₃₀ aryl or a C₂-C₃₀ heteroaryl comprising at leastone atom selected from O, S, or N in an aromatic ring.
 2. The organicelectronic device according to claim 1, wherein each of A² and A³ isindependently selected from a C₆-C₁₀ aryl or a C₂-C₁₂ heteroaryl.
 3. Theorganic electronic device according to claim 1, wherein A² and A³ areindependently selected from phenyl or pyridyl.
 4. The organic electronicdevice according to claim 1, wherein the substantially organic layercomprises an electron transport matrix compound.
 5. The organicelectronic device according to claim 4, wherein the electron transportmatrix compound comprises an imidazole or a P═O functional group.
 6. Theorganic electronic device according to claim 4, wherein the compoundaccording to formula (I) and the electron transport matrix compound arepresent in the substantially organic layer in the form of a homogeneousmixture.
 7. The organic electronic device according to claim 1, whereinthe device is selected from an organic light emitting diode, an organicsolar cell, or an organic field effect transistor.
 8. The organicelectronic device according to claim 7, wherein the device is theorganic light emitting diode, wherein the first electrode is an anode,the second electrode is a cathode, and the device further comprises alight emitting layer arranged between the anode and the cathode, andwherein the substantially organic layer is arranged between the cathodeand the light emitting layer.
 9. The organic electronic device of claim1, wherein at least one of A² and A³ is the C₂-C₃₀ heteroaryl comprisingat least one atom selected from O, S, or N in an aromatic ring.
 10. Acompound according to formula (I):

wherein A¹ is a pyridine-diyl, and each of A² and A³ is independentlyselected from a C₆-C₃₀ aryl or a C₂-C₃₀ heteroaryl comprising at leastone atom selected from O, S, or N in an aromatic ring.
 11. The compoundaccording to claim 10, wherein each of A² and A³ is independentlyselected from a C₆-C₁₀ aryl or a C₂-C₁₂ heteroaryl.
 12. The compoundaccording to claim 10, wherein A² and A³ are independently selected fromphenyl or pyridyl.
 13. The compound according to claim 10, wherein thecompound of formula (I) is selected from a lithium salt of(3-hydroxypyridin-2-yl)diphenylphosphine oxide or(2-hydroxypyridin-3-yl)diphenylphosphine oxide.
 14. An electricallydoped semiconducting material comprising at least one electron transportmatrix compound and at least one compound according to claim
 10. 15. Thecompound of claim 10, wherein at least one of A² and A³ is the C₂-C₃₀heteroaryl comprising at least one atom selected from O, S, or N in anaromatic ring.
 16. An organic electronic device comprising a firstelectrode, a second electrode, and a substantially organic layerarranged between the first and the second electrode, wherein thesubstantially organic layer comprises a compound according to formula(I):

wherein A¹ is a C₆-C₃₀ arylene or C₆-C₃₀ heteroarylene, each of A² andA³ is independently selected from a C₆-C₃₀ aryl or a C₂-C₃₀ heteroarylcomprising at least one atom selected from O, S, or N in an aromaticring, and at least one of A² and A³ is the C₂-C₃₀ heteroaryl comprisingat least one atom selected from O, S, or N in an aromatic ring.
 17. Acompound according to formula (I):

wherein A¹ is a C₆-C₃₀ arylene or C₆-C₃₀ heteroarylene, each of A² andA³ is independently selected from a C₆-C₃₀ aryl or a C₂-C₃₀ heteroarylcomprising at least one atom selected from O, S, or N in an aromaticring, and at least one of A² and A³ is the C₂-C₃₀ heteroaryl comprisingat least one atom selected from O, S, or N in an aromatic ring.